Process for continuously producing polymer electrolyte membrane and producing apparatus therefor

ABSTRACT

The present invention provides a process for producing a polymerelectrolyte membrane comprising the steps of coating a solution of a polymerelectrolyte on at least one surface of a porous substrate and laminating the coated porous substrate and a supporting material while applying a tension F (kg/cm) in a range of the following expression (A)
 
0.01≦F≦10  (A)
 
to the coated porous substrate. According to the present invention, a polymerelectrolyte composite membrane in which wrinkling and the like are suppressed and whose appearance is excellent can be continuously produced.

This application is a National Stage Application of PCT/JP2004/004068,filed Mar. 24, 2004, which claims priority from Japanese ApplicationNos. 2003-090840 and 2003-090841, both filed Mar. 28, 2003 and2003-157052, filed Jun. 2, 2003. The entire contents of each of theaforementioned applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a continuous process for producing apolymerelectrolyte membrane wherein a polymerelectrolyte is impregnatedinto voids of a porous substrate. More detail, the present inventionrelates to a continuous process for producing a polymerelectrolytemembrane characterized by coating a porous substrate with a solution ofa polymerelectrolyte and, laminating the coated porous substrate and asupporting material by using a roll while applying a tension in aspecific range to the coated porous substrate.

In addition, the present invention relates to an apparatus to beemployed for continuously producing the above-mentionedpolymerelectrolyte membrane.

BACKGROUND ART

In recent years, a fuel cell (a solid polymerelectrolyte type fuel cell)employing a polymer membrane having proton conductivity as anelectrolyte has been predominant as a use for a fuel cell of a powersource to be mounted on vehicles and the like, since such electrolyte isoperated at low temperatures, has high power density and is capable ofbeing downsized.

A method of impregnating a polymerelectrolyte into voids of a poroussubstrate has been proposed as a method for giving mechanical strength,durability and the like to a polymerelectrolyte membrane (JapanesePatent Application Laid-Open No. 6-29032).

A method of dipping a porous substrate in a solution of apolymerelectrolyte, an method for applying a solution of apolymerelectrolyte to a porous substrate and the like have been proposedas a method of impregnating a polymerelectrolyte into voids of a poroussubstrate (Japanese Patent Application Laid-Open No. 8-329962).

However, in the above-mentioned continuous processes for producing apolymerelectrolyte membrane, for example, when a porous substrate ispreviously disposed on a supporting material and coated with a solutionof a polymerelectrolyte, it is considered that swelling and slackeningare caused on the porous substrate, and consequently wrinkling and thelike are occasionally caused in appearance of a product to be obtained,resulting in deterioration external appearance.

An object of the present invention is to provide a process forcontinuously producing a polymerelectrolyte membrane in which wrinklingis suppressed and whose appearance is excellent.

DISCLOSURE OF THE INVENTION

Through earnest studies for continuously producing a polymerelectrolytemembrane in which wrinkling and the like are and whose appearance isexcellent, the present inventors have completed the present inventionthrough further various studies by finding that the object is achievedby coating a porous substrate with a solution of a polymerelectrolyte,and laminating the coated porous substrate and a supporting material byusing a roll while applying a tension in a specific range to the coatedporous substrate.

The present invention relates to a process for continuously producing apolymerelectrolyte membrane wherein a polymerelectrolyte is impregnatedinto voids of a porous substrate, namely, a continuous process forproducing a polymerelectrolyte membrane comprising the steps of: coatinga solution of a polymerelectrolyte on at least one surface of a poroussubstrate, and laminating the coated porous substrate and a supportingmaterial while applying a tension F (kg/cm) to the coated poroussubstrate in a range of the following expression (A)0.01≦F≦10  (A)

Further, the present invention provides a fuel cell and the likecomprising the polymerelectrolyte membrane obtained by theabove-mentioned process.

Also, the present invention relates to an apparatus for continuouslyproducing a polymerelectrolyte membrane, comprising a first coatingmeans for coating a solution of a polymerelectrolyte on a poroussubstrate which is being conveyed, a tension applying means for applyinga tension F (kg/cm) in a range of 0.01≦F≦10 to the coated poroussubstrate, and a laminating means for laminating a supporting materialand the porous substrate which is coated with the solution of apolymerelectrolyte and applied the tension to give a laminate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an apparatus for continuouslyproducing a polymerelectrolyte membrane, which is one of preferableembodiments of the present invention.

FIG. 2 is a schematic view of an apparatus for obtaining a laminate byfurther coating a solution of a polymerelectrolyte on thepolymerelectrolyte membrane obtained by an apparatus for continuouslyproducing illustrated FIG. 1.

FIG. 3 (a) is a cross-sectional view showing a laminate 3 b obtained inFIG. 1. FIG. 3 (b) is a cross-sectional view showing a laminate 3 eobtained in FIG. 2.

FIG. 4 is a schematic view showing an apparatus for continuouslyproducing a polymerelectrolyte membrane, which is another preferableembodiment of the present invention.

REFERENCE NUMERALS

1: a porous substrate, 2: a supporting material, 70: a solution of apolymerelectrolyte, 65: a first coating unit (a first coating means),10: a feeder (a tension applying means), 30: a laminating roll (alaminating means), 3 a, 3 b, 3 d and 3 e: laminate, 40: a drying unit (adrying means), 55: a second coating unit (a second coating means), 100and 200: apparatuses for continuously producing a polymerelectrolytemembrane

PREFERABLE MODE FOR CARRYING OUT THE INVENTION

The present invention is hereinafter detailed.

A porous substrate to be used in the present invention is a substratewhich is impregnated with a polymerelectrolyte, and is used forimproving strength, flexibility and durability of a polymerelectrolytemembrane.

The substrate is so porous as to satisfy the above-mentioned purpose ofuse, and the shape and material thereof are not limited, for example,including a porous membrane, a woven fabric, a nonwoven fabric and afibril. In the case of using a polymerelectrolyte membrane as adiaphragm of a solid polymerelectrolyte type fuel cell, the thickness ofthe porous substrate is typically 1 to 100 μm, preferably 3 to 30 μm andmore preferably 5 to 20 μm. The pore diameter of the porous substrate istypically 0.01 to 100 μm, preferably 0.02 to 10 μm, and the porositythereof is 20 to 98%, preferably 40 to 95%.

When thickness of a porous substrate is too thin, the reinforcementeffect of strength of a polymerelectrolyte membrane or the effect ofgiving flexibility and durability may be insufficient to easily causegas leakage (gas cross leak). When thickness thereof is too thick, itselectric resistance may increase, and the performance of a diaphragm maybe insufficient in the case of using an obtained polymerelectrolytemembrane as a diaphragm of a solid polymer type fuel cell. When porediameter thereof is too small, the filling of a solid polymerelectrolytemay become difficult. When pore diameter is too large, the effect ofreinforcing a polymerelectrolyte membrane may be small. When porositythereof is too low, the resistance of a polymerelectrolyte membrane mayincrease, when porosity is too high, the strength of a porous substratemay become weak to reduce the effect of reinforcing.

With regard to a porous substrate, an aliphatic polymer, an aromaticpolymer or a fluorine-containing polymer is preferably used from theviewpoint of heat resistance and the effect of reinforcing physicalstrength.

Here, examples of the aliphatic polymer include polyethylene,polypropylene, polyvinyl alcohol and an ethylene-vinyl alcoholcopolymer, and are not limited thereto. Polyethylene is a generic termof an ethylene-based polymer having repeating unit derived from ethylenein a main chain, and includes, for example, linear high-densitypolyethylene (HDPE), low-density polyethylene (LDPE) and a copolymer ofethylene and another monomer, which includes a copolymer of ethylene andan α-olefin, such as linear low-density polyethylene (LLDPE),ultra-high-molecular-weight polyethylene and the like. Polypropyleneherein described is a generic term of a propylene-based polymer havingrepeating unit derived from propylene in a main chain, and includes apropylene homopolymer, a block copolymer and a random copolymer ofpropylene and ethylene and/or an α-olefin such as 1-butene.

Examples of the aromatic polymer include polyester, polyethyleneterephthalate, polycarbonate, polyimide and polysulfone.

Examples of a fluorine-containing polymer include a thermoplastic resinhaving at least one carbon-fluorine bond in its molecule, and preferableexamples of the fluorine-containing polymer include a polymer in whichall or most of hydrogen atoms of the above-mentioned aliphatic polymerare substituted with fluorine atoms.

Examples thereof include polytrifluoroethylene, polytetrafluoroethylene,polychlorotrifluoroethylene,poly(tetrafluoroethylene-hexafluoropropylene),poly(tetrafluoroethylene-perfluoroalkyl ether) and polyvinylidenefluoride, and are not limited thereto. Among them,polytetrafluoroethylene andpoly(tetrafluoroethylene-hexafluoropropylene) are preferable, andparticularly polytetrafluoroethylene is preferable. With regard to thesefluororesins, fluororesins having an average molecular weight of 100,000or more are preferable from the viewpoint of mechanical strength.

A polymerelectrolyte to be used in the present invention is typically asolvent-soluble polymer having ion exchange groups, for example, cationexchange groups such as —SO₃H, —COOH, —PO(OH)₂, —POH(OH), —SO₂NHSO₂— and-Ph(OH) wherein Ph denotes a phenyl group, and anion exchange groupssuch as —NH₂, —NHR, —NRR′, —NRR′R″⁺ and —NH₃ ⁺ wherein R denotes analkyl group, a cycloalkyl group, an aryl group and the like. With regardto these groups, a part or all thereof may form a salt with counterions.

Examples of such a polymerelectrolyte include (A) a polymerelectrolytewherein a sulfonic acid group and/or a phosphonic acid group areintroduced into a main chain of a polymer comprising an aliphatichydrocarbon; (B) a polymerelectrolyte wherein a sulfonic acid groupand/or a phosphonic acid group are introduced into a polymer comprisingan aliphatic hydrocarbon in which a part or all of hydrogen atoms of themain chains are substituted with fluorine atoms; (C) apolymerelectrolyte wherein a sulfonic acid group and/or a phosphonicacid group are introduced into a polymer whose main chain has anaromatic ring; (D) a polymerelectrolyte wherein a sulfonic acid groupand/or a phosphonic acid group are introduced into a polymersubstantially containing no carbon atom in its main chain, such aspolysiloxane and polyphosphazene; (E) a polymerelectrolyte wherein asulfonic acid group and/or a phosphonic acid group are introduced into acopolymer comprising repeating units of any two kinds or more selectedfrom repeating units composing polymers before a sulfonic acid groupand/or a phosphonic acid group are introduced into the above-mentioned(A) to (D) polymerelectrolytes; and (F) a polymerelectrolyte whereinacidic compounds such as sulfuric acid or phosphoric acid are introducedthrough an ionic bond into a polymer containing a nitrogen atom in amain chain or a side chain.

Here, examples of the polymerelectrolyte of the above-mentioned (A)include polyvinylsulfonic acid, polystyrene sulfonic acid andpoly(α-methyl styrene)sulfonic acid.

Examples of the polymerelectrolyte of the above-mentioned (B) include apolymer having perfluoroalkyl sulfonic acid in its side chain, whosemain chain is a perfluoroalkane, such as Nafion (a registered trademarkof E.I. du Pont de Nemours Company, and so forth), a sulfonic acid-typepolystyrene-graft-ethylene-tetrafluoroethylene copolymer (ETFE, forexample, Japanese Patent Application Laid-Open No. 9-102322) wherein ahydrocarbon having a sulfonic acid group is introduced as the side chaininto the main chain made by the copolymerization of afluorine-substituted hydrocarbon vinyl monomer and a hydrocarbon vinylmonomer, and a sulfonic acid-type poly(trifluorostyrene)-graft-ETFEmembrane (for example, U.S. Pat. No. 4,012,303 and U.S. Pat. No.4,605,685) wherein α,β,β-trifluorostyrene is grafted to a polymercomprising a copolymer of a fluorine-substituted hydrocarbon vinylmonomer and hydrocarbon vinyl monomer, and a sulfonic acid group isintroduced thereto to obtain a solid polymerelectrolyte membrane.

Examples of a polymerelectrolyte of the above-mentioned (C) include apolymerelectrolyte wherein a sulfonic acid group and/or a phosphonicacid group are introduced into a polymer containing a hetero atom suchas an oxygen atom in its main chain, for example, includingpolymerelectrolytes wherein a sulfonic acid group is introduced intopolymers such as polyether ether ketone, polysulfone, polyether sulfone,poly(arylene ether), polyimide, poly((4-phenoxybenzoyl)-1,4-phenylene),polyphenylene sulfide and polyphenylquinoxalene, sulfoarylatedpolybenzimidazole, sulfoalkylated polybenzimidazole, phosphoalkylatedpolybenzimidazole (for example, Japanese Patent Application Laid-OpenNo. 9-110982), and phosphonated poly(phenylene ether) (for example, J.Appl. Polym. Sci., 18, 1969 (1974)).

Examples of a polymerelectrolyte of the above-mentioned (D) include apolymerelectrolyte wherein a sulfonic acid group is introduced intopolyphosphazene, and polysiloxane having a phosphonic acid group,described in Polymer Prep., 41, No. 1, 70 (2000).

Examples of the polymerelectrolyte of the above-mentioned (E) include apolymerelectrolyte wherein a sulfonic acid group and/or a phosphonicacid group are introduced into a random copolymer, a polymerelectrolytewherein a sulfonic acid group and/or a phosphonic acid group areintroduced into an alternating copolymer, and a polymerelectrolytewherein a sulfonic acid group and/or a phosphonic acid group areintroduced into a block copolymer. Examples of the polymerelectrolytewherein a sulfonic acid group is introduced into a random copolymerinclude a sulfonated polyether sulfone-dihydroxybiphenyl copolymer (forexample, Japanese Patent Application Laid-Open No. 11-116679).

Examples of the polymerelectrolyte of the above-mentioned (F) includepolybenzimidazole containing phosphoric acid, described in JapanesePatent National Publication No. 11-503262.

Examples of the block copolymer, in which a sulfonic acid group and/or aphosphonic acid group are introduced, included in a polymerelectrolyteof the above-mentioned (E), include a block having a sulfonic acid groupand/or a phosphonic acid group, described in Japanese Patent ApplicationLaid-Open No. 2001-250567.

The weight-average molecular weight of the polymerelectrolyte to be usedfor the present invention is typically approximately 1000 to 1000000,and the ion exchange group equivalent weight is typically approximately500 to 5000 g/mol.

The polymerelectrolyte of (C) wherein a sulfonic acid group and/or aphosphonic acid group are introduced into a polymer whose main chain hasan aromatic ring is preferably used among the above-mentioned (A) to (F)polymerelectrolytes.

The polymerelectrolyte may contain additives to be used for a polymer,such as a plasticizer, a stabilizer and a release agent.

A coating solution to be used in the present invention is a solution ofthe above-mentioned polymerelectrolyte mixed with a solvent.

A solvent to be used is not particularly limited if it can dissolve apolymerelectrolyte and be thereafter removed, for example, includingaprotic polar solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone and dimethyl sulfoxide,chlorine-based solvents such as dichloromethane, chloroform,1,2-dichloroethane, chlorobenzene and dichlorobenzene, alcohols such asmethanol, ethanol and propanol, and alkylene glycol monoalkyl etherssuch as ethylene glycol monomethyl ether, ethylene glycol monoethylether, propylene glycol monomethyl ether and propylene glycol monoethylether. These may be used singly or in a mixture of two kinds or moresolvents. Among these solvents, dimethylacetamide, a mixed solvent ofdichloromethane/methanol, dimethylformamide and dimethyl sulfoxide arepreferable from the viewpoint of solubility of the above-mentionedpolymerelectrolyte therein.

In the case of producing a polymerelectrolyte membrane by the processfor producing a polymerelectrolyte membrane as mentioned later, asolution of a polymerelectrolyte after being applied is repelled on aporous substrate and an application solution is not applied uniformly tocause solution drips, so that the thickness precision of an obtainedpolymerelectrolyte is not sufficient and stress is concentrated on athin part in thickness to easily rupture a polymerelectrolyte membrane.From such a viewpoint, with regard to preferable viscosity of a coatingsolution in the present invention, η (cps: centipoise) satisfies30≦η≦5000.

Here, viscosity η is a value measured at a relative humidity of 50% orless by using a BL type viscometer (manufactured by Tokyo Keiki Co.,Ltd.). The viscosity is more preferably 100≦η≦3000, most preferably300≦η≦1500.

The concentration C (% by weight) of a coating solution is preferably 1or more, more preferably 6 or more from the viewpoint that apolymerelectrolyte is sufficiently impregnated into voids of a poroussubstrate when a coating solution is dried. The concentration ispreferably 50 or less, more preferably 35 or less from the viewpoint ofcontrolling coating thickness.

A polymerelectrolyte is impregnated into voids of a porous substrate byusing the above-mentioned solution of a polymerelectrolyte as a coatingsolution to coat a porous substrate therewith. Here, a coating method ispreferred to be a method capable of achieving desired coating thickness,for example, including a method employing a roll coater, a comma coater,a doctor blade coater, a lip coater, a wire bar, a gravure coater, a barcoater and the like, a method of casting, called a casting method, byextruding a coating solution from a die and the like set at a desiredclearance so as to get desired coating thickness, and a method ofimmersing a porous substrate in a coating solution.

In the case of coating one surface of a porous substrate or one surfaceof the after-mentioned supporting material with a coating solution, thecoating is preferred to be performed by at least one selected from theabove-mentioned methods. In the case of coating both surfaces of aporous substrate, a coating method includes a method where coating onlyone surface is performed and coating the other surface is performedafter white, and a method of coating both surfaces simultaneously. Amethod of coating both surfaces of a porous substrate simultaneously orseparately includes a method of coating in a combination of theabove-mentioned coating methods, such as a combination of a methodemploying a coater and a method of casting, a method of immersing in acoating solution to thereafter adjust a thickness through a gap set at adesired clearance, and the like.

In the case of coating a coating solution on a porous substrate, whichis not coated with a coating solution, the coating is performed in astate such that a porous substrate does not contact with a supportingmaterial. Thereafter, a supporting material and the coated poroussubstrate are laminated while applying a tension F (kg/cm) in a range ofthe following expression (A)0.01≦F≦10  (A)to the coated porous substrate.

The laminating while applying the above-mentioned tension preventswrinkling and the like from being caused in appearance of a product, andallows a product excellent in appearance to be continuously produced.Examples of the laminating method include a laminating method by a rolland the like.

In the case where the tension F is out of the above-mentioned range,swelling, slackening and the like of a porous substrate causes poorappearance such as wrinkling on the surface of an obtainedpolymerelectrolyte. The tension F is preferably 0.05 or more, morepreferably 0.1 or more, and preferably 2 or less, more preferably 1 orless.

In the case of coating again a coated porous substrate as describedabove, the coating can be performed in either state of contact with asupporting material and noncontact therewith.

A polymerelectrolyte is impregnated into voids of a porous substrate bydirectly applying an application solution to a porous substrate disposedon a supporting material. A polymerelectrolyte may be impregnated intovoids of a porous substrate by previously applying an applicationsolution onto a supporting material to thereafter laminate a poroussubstrate thereon, or a polymerelectrolyte may be impregnated into voidsof a porous substrate by further applying on the other surface of aporous substrate after laminating. In the case of applying anapplication solution to a porous substrate, the applying may beperformed again after drying, or applying and drying may be repeatedplural times.

A coating solution having a contact angle of 90° or less with respect toa porous substrate is preferable by reason of having the effect ofsiphoning a solution of a polymerelectrolyte by a capillary phenomenon,and thus a coating solution is filled almost completely into voids of aporous membrane. As a result, coating and drying by using a coatingsolution of at least a required quantity provide a composite of a porousmembrane wherein a polymerelectrolyte is impregnated almost completelyinto voids of a porous membrane, and additionally a layer comprising apolymerelectrolyte.

The required quantity of a coating solution is, for example, thequantity of a coating solution containing equal to or more than aquantity of a polymerelectrolyte equivalent to void volume existing in aporous substrate in a predetermined coating range. The void volume of aporous substrate can be calculated from thickness, coating area andapparent density of the substrate, the density of a raw materialcomposing the substrate, and the like.

A supporting material laminated on a porous substrate includes, forexample, a sheet comprising a polymer except a polymerelectrolyte of thepresent invention, having no ion exchange group, and other sheets madeof metal and made of glass, which supporting material is notparticularly limited if it is not swelled nor dissolved by theabove-mentioned coating solution and a membrane obtained after beingproduced can be peeled thereoff. A preferable supporting material is asupporting material which can be transformed while following a membraneobtained after being produced, above all, preferably a sheet comprisingthe polymer except a polymerelectrolyte described in the presentinvention, having no ion exchange group. For example, a sheet comprisingpolyolefin resins such as polyethylene and polypropylene, polystyrene(PS), polycarbonate (PC), and polyethylene terephthalate (PET) isappropriately used as the above-mentioned sheet comprising a polymer nothaving an ion exchange group. The supporting material may be subject toreleasing treatment, mirror treatment, embossing treatment, delusteringtreatment or the like as required.

In the case where an electrolyte membrane of the present invention isused as an electrolyte membrane for a fuel cell joined with an electrode(MEA), a carbon woven fabric and a carbon paper to which a catalyst tobe used as an electrode is previously applied are preferably used as asupporting material from the viewpoint of omitting the steps of peelinga multilayer polymerelectrolyte off a supporting material and joining anelectrode and the like.

In the case of laminating a supporting material as described above on aporous substrate whose one surface is coated, a supporting material maybe laminated on an uncoated surface thereof, and is preferably laminatedon a coated surface. Here, a supporting material coated with a coatingsolution can also be used, and in the case of using this, a surface of aporous substrate to be laminated may be coated or not coated, preferablynot coated.

In the case of laminating a supporting material, the tension ispreferably applied to also a supporting material. Tension to asupporting material is preferred to be such a tension or more as not toslacken a supporting material, which is preferred to be laminated atsuch a tension or less as not to be ruptured on a porous substrate intowhich a solution of a polymerelectrolyte is filled.

Examples of a laminating method include a method of laminating coatedporous substrate and supporting material while being along a roll and amethod of passing between a pair of rolls set at desired clearance.

In the present invention, after laminating the coated porous substrateand supporting material, a porous substrate and a coated poroussubstrate may be further laminated as required, and a laminating methodthereof also includes the above-mentioned methods.

A drying method is not particularly limited if it is a method forsufficiently removing a solvent from a porous substrate coated with anapplication solution, for example, including an indirect heating systememploying microwaves, high-frequency waves, far-infrared rays, a hot-airheater, steam, a heating furnace and the like, and a direct heatingsystem employing a thermal transfer roll and the like. An indirectheating system by a hot-air heater and a heating furnace is preferableby reason of being inexpensive in view of equipment.

The drying is typically performed at temperatures at which a solvent canbe sufficiently removed and a supporting material is not transformed.

In the case where a polymerelectrolyte is not sufficiently impregnatedinto voids of a porous substrate after drying and an electrolyte layerneeds to be provided for an outermost layer, a solution of apolymerelectrolyte may be applied and dried again after theabove-mentioned step of drying.

A polymerelectrolyte membrane of the present invention is obtained bythe above-mentioned methods, and examples of the layer constitutionthereof include [a composite layer/an electrolyte layer/a supportingmaterial layer], [an electrolyte layer/a composite layer/a supportingmaterial layer] and [an electrolyte layer/a composite layer/anelectrolyte layer/a supporting material layer], and further[anelectrolyte layer/a composite layer/an electrolyte layer/a compositelayer/an electrolyte layer/a supporting material layer], which is asuperposition of the above-mentioned layer constitution, is also one ofpreferable layer constitutions. Such a polymerelectrolyte membrane maybe used with a supporting material peeled off in the case of being usedfor a fuel cell.

With regard to a polymerelectrolyte membrane, the thickness thereof istypically approximately 5 to 200 μm, preferably approximately 10 to 100μm, and more preferably approximately 15 to 80 μm.

Next, a fuel cell employing this is described.

A fuel cell is composed in such a manner that a unit cell, which iscomposed of a membrane electrode assembly comprising an anode and acathode as gaseous diffusion electrodes disposed opposite to each otherand a polymerelectrolyte interposing between both of the electrodeswhile contacting therewith to pass ions selectively, is alternatelylaminated in plural pieces through a separator provided with a gascirculating means. In this fuel cell, electric power generation isperformed by utilizing an electrochemical reaction caused by supplyingfuels such as hydrogen, reformed gas and methanol to an anode and anoxidizing agent such as oxygen to a cathode, that is, in such a mannerthat the fuels are electrocatalytically oxidized and simultaneously theoxidizing agent is electrocatalytically reduced to convert chemicalreaction energy directly into electric energy.

The catalyst is not particularly limited if it can activate anoxidation-reduction reaction with hydrogen or oxygen; conventionalcatalysts can be used and particulates of platinum are preferably used.Particulates of platinum are frequently used preferably in a state ofbeing supported with particles of activated carbon or graphite, or withfibrous carbon.

Conventional materials can be used with regard to anelectrically-conductive substance as a current collector, and porouscarbon woven fabric or carbon paper is preferable in order toefficiently transport raw material gas to a catalyst.

A conventional method such as a method described in J. Electrochem.Soc.: Electrochemical Science and Technology, 1988, 135(9), 2209 can beused with regard to a method for joining platinum particulates or carbonsupporting platinum particulates to porous carbon woven fabric or carbonpaper and a method for joining it to a polymerelectrolyte sheet.

Next, an apparatus for continuously producing a polymerelectrolytemembrane of the present invention is described. FIGS. 1 and 2 areschematic views showing an apparatus 100 for continuously producing apolymerelectrolyte composite membrane, which is one of preferableembodiments (a first embodiment).

This apparatus 100 for continuously producing is an apparatus forcontinuously producing a polymerelectrolyte membrane by coating aflexible porous substrate 1 with a solution 70 of a polymerelectrolyteto thereafter superpose on a flexible supporting material 2 and form alaminate 3 a and then dry this laminate 3 a.

This apparatus 100 for continuously producing has, mainly, as shown inFIG. 1, a feeder 10 for feeding the porous substrate 1, a feeder 20 forfeeding the supporting material 2, a first coating unit (a first coatingmeans) 65 for coating the porous substrate 1 fed from the feeder 10 withthe solution 70 of a polymerelectrolyte, a laminating apparatus (alaminating roll in the Figure) 30 for superposing and laminating theporous substrate 1 coated with the solution 70 of a polymerelectrolyteand the supporting material 2 fed from the feeder 20 to form thelaminate 3 a, a drying unit (a drying means) 40 for drying the laminate3 a, and a wind-up machine 80 for winding up the dried laminate 3 a.

The feeder 20 has a bobbin 20 a on which the supporting material 2 iswound up, and the rotation of this bobbin 20 a allows the supportingmaterial 2 to be fed. The supporting material 2 fed from the feeder 20is fed to the laminating apparatus 30 under the guidance of a guideroller 21.

The feeder 10 can be mounted with a bobbin 10 a on which the poroussubstrate 1 is wound up, and the rotation of this bobbin 10 a allows theporous substrate 1 to be fed. The porous substrate 1 wound out from thefeeder 10 passes through the first coating unit 65 under the guidance ofguide rollers 11 and 12 and is thereafter fed to the laminating means30.

The first coating unit 65 has a pair of cylindrical horizontal rollers13 and 14, which are disposed in a horizontal direction and are parallelto each other and can rotate around a horizontal axis, and the poroussubstrate 1 to be coated is hung on the upper end of each of thehorizontal rollers 13 and 14, and is horizontally conveyed between thesehorizontal rollers 13 and 14. The first coating unit 65 has a slot die60 for coating the porous substrate 1 horizontally conveyed by thesehorizontal rollers 13 and 14 with the solution 70 of apolymerelectrolyte from above.

This slot die 60 has an opening 60 a of a predetermined rectangularshape extending in a width direction of the porous substrate 1 at thelower end facing the porous substrate 1. This slot die 60 pushes eachpredetermined quantity of the solution 70 of a polymerelectrolyte fedfrom a polymerelectrolyte feeding apparatus 62 out of the opening 60 ato coat the porous substrate 1 in a belt-like state.

Here, with regard to the coated quantity of the solution 70 of apolymerelectrolyte to coat with, supply pressure, a shape of the opening60 a and the like are set so that a desired thickness is obtained afterdrying. The slot die 60 coats the porous substrate 1 before being fed tothe laminating roll 30 with the solution 70 of a polymerelectrolyte.

The laminating means 30 is a body of rotation, which has a cylindricalshape and rotates around a horizontal axis, and conveys the supportingmaterial 2 and the porous substrate 1 while being along acircumferential surface thereof to form the laminated body 3 acomprising the porous substrate 1 superposed on the supporting material2. Here, the supporting material 2 contacts with the laminating roll 30.

The above-mentioned slot die 60 applies the solution 70 of apolymerelectrolyte to a surface on the side of the porous substrate 1contacting with the supporting material 2 in the step of laminating inthe laminating roll 30.

This producing apparatus 100 is composed so that the laminate 3 a isconveyed along a circumferential surface of the laminating roll 30 andthereafter passes through the drying unit 40 under the guidance of guiderollers 31, 32, 33, 34, 35, 36, 37 and 38 and then is fed to the wind-upmachine 80.

The drying unit (the drying means) 40 has plural dryers 40 a for blowinghot air over from the porous substrate 1 side of the laminate 3 a guidedby the guide rollers 31 to 38, and plural dryers 40 b for blowing hotair over from the supporting material 2 side of this laminate 3 a to drythe laminate 3 a, thus obtaining a laminate 3 b. The conveyance lengthin the drying unit 40 is, for example, approximately 5 to 6 m.

In the embodiment, the laminating means 30 and the guide rollers 31 to38, which contact with the laminate 3 a before completing drying,contact with the supporting material 2 side of the laminate 3 a, so thatthe solution 70 of a polymerelectrolyte is prevented from attaching toeach of the rollers.

The wind-up machine 80 has a bobbin 80 a for winding up the driedlaminate 3 b, which is wound up by rotating this bobbin 80 a at apredetermined rate. The wind-up rate is typically approximately 1 m/min,depending on the solvent to be used.

In the apparatus 100 for continuously producing a polymerelectrolytecomposite membrane according to the embodiment, the feeder 10 and thefeeder 20 rotate the bobbin 10 a and the bobbin 20 a in accordance withthe wind-up action of the wind-up machine 80 as described above to sendout the porous substrate 1 and the supporting material 2, respectively.Here, the feeder 10 and the feeder 20 apply a desired tension F in aconveyance direction to each of the porous substrate 1 and thesupporting material 2 by adjusting rotational torque required forrotating these bobbins 110 a and 20 a. That is, in the embodiment, thefeeder 10 and the feeder 20 perform the function of a means of applyinga tension. Specifically, this tension F is, as described above, 0.01kg/cm or more and 10 kg/cm or less, preferably 0.05 or more, morepreferably 0.1 or more, and preferably 2 or less, more preferably 1 orless.

In addition, with regard to a apparatus 200 for continuously producingof a second embodiment, as shown in FIG. 4, the bobbin 80 a on which thedried laminate 3 b was wound up can be mounted again on the feeder 10.The feeder 10 can feed the dried laminate 3 b to the laminating means 30through a second coating unit 55.

The second coating unit (the second coating means) 55 has theabove-mentioned horizontal rollers 13 and 14 in common with the firstcoating unit 65. With regard to these horizontal rollers 13 and 14, thedried laminate 3 b to be coated can be hung on the lower end of each ofthe rollers and then be horizontally conveyed. Here, the feeder 10 feedsthe dried laminate 3 a to the second coating unit 55 so that the side ofthe supporting material 2 of the dried laminate 3 a contacts with thehorizontal rollers 13 and 14, that is, the porous substrate 1 faces thebottom side of the Figure.

The second coating unit 55 is provided with a gravure roll 50 forcoating the porous substrate 1 of the dried laminate 3 b horizontallyconveyed by the horizontal rollers 13 and 14 with the solution 70 of apolymerelectrolyte from below, and a pan 52 for feeding the solution 70of a polymerelectrolyte to this gravure roll 50.

A laminate 3 d further coated with the solution 70 of apolymerelectrolyte by this second coating unit 55 is wound up by thewind-up machine 80 under the guidance of the laminating means 30 and theguide rollers 31 to 38 through the drying unit 40.

Here, the laminating means 30 and the guide rollers 31 to 38, whichcontact with the laminate 3 d, contact with the side of the supportingmaterial 2 of the laminate 3 d, so that the solution 70 of apolymerelectrolyte before drying is prevented from attaching to each ofthe rollers.

Next, the function in the apparatus 100 for producing is described.

As shown in FIG. 1, the top surface of the porous substrate 1 fed fromthe feeder 10 is coated with the solution 70 of a polymerelectrolytefrom the slot die 60 of the first coating unit 65. The above-mentionedpredetermined tension F is applied to this porous substrate 1 by thefeeder 10. The coated surface of the porous substrate 1 to which thistension is applied is superposed on the supporting material 2 in thelaminating means 30, and the porous substrate 1 and the supportingmaterial 2 stick to each other to form the laminate 3 a.

This laminate 3 a is conveyed through the drying unit 40. On thisoccasion, a solvent in the solution 70 of a polymerelectrolyteimpregnated into voids of the porous substrate 1 is removed, so that thepolymerelectrolyte is filled into voids to obtain a dried poroussubstrate 1A and additionally a layer of the polymerelectrolyte 70 isdried and formed into a polymerelectrolyte layer 70A, and then such adried laminate 3 b is wound up on the bobbin 80 a of the wind-up machine80. This laminate 3 b is a polymerelectrolyte membrane having astructure of [a composite layer/an electrolyte layer/a supportingmaterial layer] (refer to FIG. 3( a)).

According to the embodiment, the above-mentioned predetermined tension Fis applied to the porous substrate 1 coated with the solution 70 of apolymerelectrolyte, so that the porous substrate 1 and the supportingmaterial 2 are laminated in a state such that swelling and slackening ofthe porous substrate 1 are sufficiently restrained, and consequentlypoor appearance such as wrinkling of the porous substrate 1A is reducedin the dried laminate 3 b. Thus, the adoption of such a laminated body 3b as a polymerelectrolyte membrane in a fuel cell and the like asdescribed above realizes the improvement of lifetime and the like.

The first coating unit 65 coats a surface of the porous substrate 1, onwhich the supporting material 2 is laminated, with the solution of apolymerelectrolyte, so that the porous substrate 1 and the supportingmaterial 2 adhere favorably in the laminate 3 a.

This apparatus 100 for producing is provided with the drying unit 40 fordrying the laminate 3 a, whereby mass production of the laminate 3 b asa dried polymerelectrolyte membrane can be performed appropriately.

Subsequently, as shown in FIG. 2, the bobbin 80 a on which the driedlaminate 3 b is wound up is mounted on the feeder 10, and the driedlaminate 3 b is hung on the lower ends of the horizontal rollers 13 and14 so that the porous substrate 1A is on the bottom side while a desiredtension is applied thereto, and additionally is conveyed to a laterstage through the laminating means 30. Here, the solution 70 of apolymerelectrolyte is applied on a surface of the porous substrate 1A ofthe dried laminate 3 b from the gravure roll 50 of the second coatingunit 55, and the laminate 3 d to which this solution was applied isfurther dried in the drying unit 40 to form the polymerelectrolyte layer70A by the drying of the solution 70 of a polymerelectrolyte, thusforming a laminate 3 e. This laminate 3 e is a polymerelectrolytecomposite membrane having a structure of [an electrolyte layer/acomposite layer/an electrolyte layer/a supporting material layer] (referto FIG. 3( b)).

According to this, the second coating unit 55 for further coating theporous substrate 1A in the laminate 3 b once dried with the solution ofa polymerelectrolyte is provided, whereby a polymerelectrolyte membranehaving a structure of [an electrolyte layer/a composite layer/anelectrolyte layer/a supporting material layer] can be producedappropriately.

Next, a apparatus 200 for continuously producing a polymerelectrolytecomposite membrane is described. The apparatus 200 for producingaccording to the embodiment differs from the apparatus 100 for producingin that the second coating unit (the second coating means) 55 coats theundried laminate 3 a after being laminated in the laminating means 30with the solution 70 of a polymerelectrolyte.

Specifically, the second coating unit 55 has a pair of horizontalrollers 113 and 114 for horizontally conveying the laminate 3 a formedby the laminating means 30 while hung on the lower ends thereof. Thesehorizontal rollers 113 and 114 are provided independently of thehorizontal rollers 13 and 14 of the first coating unit 65.

The gravure roll 50 coats the laminate 3 a horizontally conveyed by thehorizontal rollers 113 and 114 with the solution 70 of apolymerelectrolyte from below to form a laminate 3 f in which bothsurfaces of the porous substrate 1 are coated with the solution 70 of apolymerelectrolyte.

According to such an apparatus 200 for producing, in addition to theeffect of functions in a first embodiment, a surface (the bottom side)of the porous substrate 1 in the laminate 3 a, which is not coated withthe solution 70 of a polymerelectrolyte, is also coated with thesolution 70 of a polymerelectrolyte by the gravure roll 50, whereby apolymerelectrolyte membrane having a structure wherein [an electrolytelayer/a composite layer/an electrolyte layer/a supporting materiallayer] can be easily produced by one time of the step of drying.Further, the bottom surface of the porous substrate 1 is coated with thesolution 70 of a polymerelectrolyte after being made into the laminate 3a, so that the effect of restraining wrinkling in the porous substrate 1is high as compared with the case where the bottom surface of the poroussubstrate 1 whose top surface was coated is further coated with thesolution 70 of a polymerelectrolyte before being made into the laminate3 a.

Here, in the above-mentioned embodiment, the first coating unit 65 andthe second coating unit 55 are provided with the slot die 60 and thegravure roll 50 respectively, and other means than the above-mentionedcoating means may be used.

In the above-mentioned second embodiment, the second coating unit 55coats the porous substrate 1 of the laminate 3 a after being laminatedin the laminating roll 30 with the solution 70 of a polymerelectrolyte,and the apparatus 200 for producing can operate even though the bottomsurface and the like of the porous substrate 1 whose top surface wascoated in the first coating unit 65 are coated with the solution 70 of apolymerelectrolyte before being laminated in the laminating means 30.

EXAMPLES

The present invention is hereinafter described by referring to examplesand is not limited thereto.

<Evaluation of Appearance of a Polymerelectrolyte Composite Membrane>

A sheet of sample having a size of 20 cm×20 cm was cut out of thecentral portion of a polymerelectrolyte composite membrane, and ananother sheet having a size of 20 cm×20 cm was cut out of the centralportion corresponding to the position as the sample previously cut outat a spot 1 m away in a wind-out direction from the spot of previouslycutting out. In these two sheets of composite membrane samples, thesupporting material was peeled off to confirm the number of visuallyobservable wrinkles. A higher value thereof signifies poorer appearance,while a lower value signifies more favorable appearance.

<Thickness Unevenness>

A sheet having a size of 20 cm×20 cm was cut out of a polymerelectrolytecomposite membrane, and the supporting material was peeled off tomeasure the thickness at intervals of 1 cm in each of MD and TDdirections. An average value thereof was denoted as T, the largest valueof thickness among measuring points was denoted as Tmax, and thesmallest value of thickness was denoted as Tmin to calculate a value ofthe following expression.(Tmax−Tmin)/T

The higher the value of this, the poorer the thickness precision, whilethe lower the value, the more the favorable thickness precision.

<Evaluation of Fuel Cell Performance>

A platinum catalyst supported with fibrous carbon and a porous carbonwoven fabric as a current collector were joined to both surfaces of amultilayer polymerelectrolyte composite membrane off which thesupporting material was peeled. Humidified oxygen gas was blown on onesurface of the unit and humidified hydrogen gas on the other surfacethereof to repeat the processes of operation and stop, for 1 week andmeasure electric power generation properties of the assembly.

<Porous Substrate and Supporting Material>

A porous membrane made of polyethylene (a membrane thickness of 14 μm, awidth of 30 cm, a porosity of 57%) was used as a porous substrate, andpolyethylene terephthalate (PET) manufactured by Toyobo. Co., Ltd.(COSMOSHINE A4100: a thickness of 100 μm, a width of 30 cm) was used asa supporting material.

Reference Example 1 Manufacture Example of a Polymerelectrolyte

According to a method described in Japanese Patent Application Laid-OpenNo. 2001-250567, a block copolymer comprising a polyether sulfonesegment and a poly(2-phenyl-1,4-phenylene oxide) segment was synthesizedand thereafter sulfonated.

Example 1

The sulfonated block copolymer obtained in Reference Example 1 wasdissolved in N,N-dimethylacetamide so as to have a concentration of 15%by weight to prepare a solution. The viscosity η of the solution was 710cps as a result of measuring by a BL type viscometer manufactured byTokyo Keiki Co., Ltd. One surface of the porous membrane made ofpolyethylene was coated with the obtained solution so as to have athickness of 150 μm while applying a tension of 0.1 (kg/cm) thereto by agravure coater, and laminated in a state of the same tension on the PETto which a tension of 0.03 (kg/cm) was applied so that the coatedsurface side contacted with the PET, and then dried in a drying furnaceset at a temperature of 80° C. to obtain a polymerelectrolyte membranecomprising (a composite layer/an electrolyte layer/a supportingmaterial). The evaluation of appearance as well as the evaluation offuel cell properties was performed to show the results in Table 1.

Example 2

One surface of the porous membrane made of polyethylene was coated withthe solution of a polymerelectrolyte used in Example 1 so as to have athickness of 150 μm while applying a tension of 0.1 (kg/cm) thereto by agravure coater, and laminated in a state of the same tension on the PETto which a tension of 0.03 (kg/cm) was applied so that the coatedsurface side contacted with the PET, and then dried in a drying furnaceset at a temperature of 80° C. After then, a surface of the porousmembrane on which the PET was not laminated was coated again in the samemanner and dried in a drying furnace set at a temperature of 80° C. toobtain a polymerelectrolyte membrane comprising (an electrolyte layer/acomposite layer/an electrolyte layer/a supporting material). The resultsof evaluation were shown in Table 1.

Example 3

Both surfaces of the porous membrane made of polyethylene were coatedwith the solution of a polymerelectrolyte used in Example 1 so as tohave a thickness of 150 μm each while applying a tension of 0.1 (kg/cm)thereto by using a gravure coater and a die, and laminated in a state ofthe same tension on the PET of Reference Example 2 to which a tension of0.03 (kg/cm) was applied, and then dried in a drying furnace set at atemperature of 80° C. to obtain a polymerelectrolyte membrane comprising(an electrolyte layer/a composite layer/an electrolyte layer/asupporting material). The results of evaluation were shown in Table 1.

Comparative Example 1

Coating was conducted in the same manner as in Example 1 and directlydried in a drying furnace without being laminated on a supportingmaterial to obtain a polymerelectrolyte membrane comprising (anelectrolyte layer/a composite layer). The results of evaluation wereshown in Table 1.

TABLE 1 External Appearance (the number of wrinkles) Fuel CellProperties Example 1 0 *1 Example 2 0 *1 Example 3 0 *1 ComparativeExample 1 12 *2 *1: Neither gas leak nor deterioration of properties wasobserved. *2: Gas leak was caused and deterioration of properties wasobserved.

INDUSTRIAL APPLICABILITY

According to the present invention, a polymerelectrolyte compositemembrane in which wrinkling and the like are suppressed and whoseappearance is excellent can be continuously produced by coating a poroussubstrate with a solution of a polymerelectrolyte to thereafter laminatethe coated porous substrate and a supporting material with the use of aroll while applying a tension F (kg/cm) in a specific range of 0.01≦F≦10to the coated porous substrate.

The invention claimed is:
 1. A process for producing a polymerelectrolyte membrane comprising the steps of: coating a solution of apolymer electrolyte on at least one surface of a porous substrate; andlaminating the coated porous substrate with a supporting material whileapplying a tension F (kg/cm) in a conveyance direction in a range of thefollowing expression (A)0.01≦F≦10  (A) to the coated porous substrate.
 2. The producing processaccording to claim 1, wherein the supporting material is laminated on acoated surface of the coated porous substrate.
 3. The producing processaccording to claim 1, wherein a surface of the supporting material to belaminated on the porous substrate is previously coated with the solutionof a polymer electrolyte.
 4. The continuously producing processaccording to claim 1, wherein a viscosity η (cps) of the solution of apolymer electrolyte is in a range of 5≦η≦5000.
 5. The producing processaccording to claim 1, wherein a concentration C (wt %) of the solutionof a polymer electrolyte is 1≦C≦50.
 6. A polymer electrolyte membraneobtained by the process according to claim
 1. 7. A fuel cell comprisingthe polymer electrolyte membrane according to claim 6.